Means for preventing ice accumulation on airfoils



B. lF. JONES June 3, 1952 MEANS FOR PREVENTING im; 1101211111111111101115N-l AIRgoILs Filed July 31, 1945 2 SHEETS-SHEET 1 June 3, 1952 B F, JONES 2,599,059

MEANS FOR PREVENTING ICE ACCUMULATION ON AIRFOILS Patented `une 3, 1952` MEANS Fon PREVENTING ICEACCUMULA- 'rIoN 0N AIRFOILS Benjamin F. Jones, Akron, Ohio, assigner to The B. F. Goodrich Company, New York, N. Y., a corporation of New York Application July 31, 1945, Serial N0. 608,066

9 Claims.

The invention relates to protective coverings for preventing the accumulation of ice on the leading edges of airfoils and other exposed surfaces, and especially to such coverings having inilating and heating actions for ice-removal and prevention purposes.

Prior constructions of coverings generally having inflatable tubes in a central zone and stretchable portions extending rearwardly therefrom, have not been Wholly satisfactory under some icing conditions in preventing objectionable icedeposits on the leading edges of wings and other airfoils. Also, the prior inflatable coverings have been generally attached only along their margins to the wings or other airfoils thereby permitting objectionable lifting of intermediate portions of the coverings at regions of relatively low pressure rearwardly of the leading edges, and such coverings have presented the difficult problem of venting beneath the coverings to prevent objectionable bulging.

Prior constructions of coverings having heating action only for ice-removal purposes have likewise not been wholly satisfactory under some icing conditions in preventing objectionable ice-deposits thereon. Also, such heated coverings generally have one or more other disadvantages such, for example, as aerodynamic and thermal inefliciency, complicated and heavy construction, excessive electrical power requirement necessitating objectionably large and heavy generators, objectionable heat losses to the airplane structure, and objectionable run-back or flow-back of water from melted ice at the leading edge of an airfoil flowing rearwardly and refreezing on the covering aft of the heating zone.

Variation in the character of ice-deposits or formation such as glaze, rime or rime frost on the airfoils adds to the difficulty of effectively preventing the accumulation of ice atv the leading edges, as each form of ice presents distinct problems of removal. Also, the bond of adhesion of the ice to the covering has been found to increase as the air temperature is decreased, i. e., relatively high adhesion is encountered at low temperatures, which further increases the difficulty of effective ice-removal for the several species of ice-deposits.

Objects of the invention are to provide for effectively overcoming such disadvantages and difficulties of the prior constructions and for promptly and thoroughlyremoving ice-deposits from the leading edges of airfoils and other exposed surfaces; to provide for combined inflating-and heating yactions `effective in apparatus or protective coverings for ice-removal and prevention purposes; to provide for breaking ,ther bond of types of ice which heretofore have been j diiicult to remove; to provide for a configuration of surface deformations together with a heated zone or zones in a covering for breaking and removing the ice-deposit thereon under a wide variety of icing conditions; to provide for stability of heating action at one orV more zones; and to provide simplicity and thinness of construction, convenience of manufacture and installation and for effectiveness ofvoperation.

Other objects of the invention are to provide for preventing the entrapment of air beneath the covering and the lifting of the covering away from the airfoil or other structure at regions of low pressure; to provide for overcoming now-back to the rearward regions of such covering; and to provide for maintaining the aerodynamic characteristics of the airfoil.

More specific objects of the invention are to provide for distending and stretching a portion y of the covering and for heating an adjacent portion of such covering; to provide for such distention and stretching at one or more spanwiseextending lZones of the covering and for electrical heating at one or more other spanWise-extendin'g zones of the covering; to provide for a surfaceconguration of one or more portions of the covextent of a distensible portion; to provide for cyclical distension and heating actions respectively at spaced-apart regions substantially throughout the Whole extent of the covering; and to provide Afor heating temperatures at one ormore zones of the covering effective for ice-removal and prevention purposes and/or in accordance with the thicknessof the ice-deposit immedi- Y ately at such zones.

These and other objects and advantages of the invention will be apparent from the following deL-*I scription. Y

In the accompanying drawings, whichform a part of this specification, and in which like nudesignate like parts merals are employed to throughout the same: Fig. 1 is a perspective view from above of a protective covering mounted upon the leading edge* of a Wing of an aircraft and constructed in accordance with and embodying the invention, parts being broken away;

Fig. 2 is a plan view from above of the protective covering shown in Fig. 1 before its attachment to a wing, parts being broken away;

Fig. 3 is a sectionalview taken along line 3-3 y Fig. 6 is a view like Fig. 2y showinganotliei;n

modified construction of the protectiveicveririg,v

parts being broken away; and

Fig. 7 is a view like Fig. 2 "showing a further modification of the protective; covering; parts. being broken away.

To the ends of eifectively removingl 5.6: de posited at the leading edge of an airfoil or other surface exposed to'ow of air under icingconditions, the inventionfprovides apparatus corn- Drielie. eovoros of elastic materiel for the leading dge yhaving distending and stretchingv anskulieating actions intermediate opposite marginsof the covering; and such apparatus includes means' for locally distending and stretching the to a surface-configuration eiective to loosen, and break ice deposited thereon and men'ferheetine the ooverineto temperatures effective i015 ite-,removal Purposes "The oorsbiifos hotties and disteudine and stretchingac -v ilS of the1 o re rii1e Cooperate in effecting icereznovalffrom such leading edge by providing Slilfloieot heat to prevent the formation of ice arid. E VePQre' the Water droplets, by melt..-

ing the oefot the bonded interface between the ioofagnd'the devoting, effectively breaking. the adhesivegbond of the ice, orby preventing thefreezins. o fleuperfoooled voter droplets etsuoh heetingwzone, and also by stressing, the icev deposit. together with so distending the surface of; said @QT/161.39% s iloh, that the. bond ofthe ioe at the distersibls YZone is. broken effectively, and t heficefrieeton loosened and/or broken for. removal?. btbesoereigngeotion of the flow of. air across. theoorerine, The distending action; may ooaot. additionallvwitn the heating action inriifting the oosoned-ice-formation, especially atv e roer.- Wers. 'h eatinsfportion, and moving outwardly suchice into thejairstream forremoyal purposes. anV illustrative embodiment of; the invention shown especially in Figs. 1, Zand 3the construcg Vcludes ga covering I5., ofv elastic material.

g Y rV example, as resilient rubber or `otherA rubber We material |5ct positionableV about the leadingedgeofa wing I6 for'an aircraft,which may-be. ofthe heayier-than-air type having one;

,ormoreengines (notshown) mounted in one or' more nacelles l'l'for rotatively drivingpne orV more propellers I8. The covering `l5 may be positionedV upon other surfaces of ithe aircraft terioration from heat.

4 tend rearwardly from thecentral heating zone substantially to the respective spanwise margins 20, 2l. The rubber material at the inner face of the covering desirably has heat and electrical insulating characteristics forY minimizing heat losses by conduction to the material of the wing and for electrically isolating the Ycovering from the Wing.

At the central zone of the covering i5 is a flexible heating element 24.substantially coextensive therewith for producing the desired temperatures effective for ice-removal purposes. The

heating element 24 is preferably imbedded in the rubber body I5kntermediate the inner and outer faces ofthe 'covering I5 as shown especially in "Fig '3, and facilitates obtaining eiective and substantial stabilityI of heating action throughout the central' z'one I9. Y

The' heating element 24 is constructed preferably of stretch-resisting vwoven fabric sheet material of cotton, glass-fiber, nylon, rayon or other suitable lamentary material having the characteristics of little or no electrical conductivity, relatively high strength, and resistance to Cie- Electrically conductive resilient composition including suitable rubberlike material having particles of acetylene black, channel' black, graphite or other. suitable conductive substance therein, is coatedV or spread as in paste or semi-liquid form desirably on both sides ofthe woven fabric. Each coating is relatively thin and inV electrical contact with the` otlfierjby` virtue of the penetration of such con'- 'ductive composition through the interstices of such; for example, as the leading edges 'oflthe'V empennagefmembers', propellerv blades, struts,

' heating zone, which distensibleportions also exil ythe woven fabric and' to some extent into' the threads of the latter, fabric. One or more'thin coats or layersA of the conductive composition may be spread in superimposed relation on the respective sidesof.- the woven fabric sheet. to provide the desired uniformity of thickness and uniformity of conductivity, whereby a nner adjust-v ment of vsuch conductivity may be obtained as compared to that obtained. by-painting or calendering: the wovenfabric with the conductive composition. Such construction of the heating -airfoill and.A a heating elementcapable .of` being integrally bonded and- 'united with the rubber body |541 of the covering.

The heatingarrangement sl'iown` especially in Figs. 2fand 3 mayrhaveadoublelayer or thickness of fabric reinforced-electrically conductive composition at spaced-apart rearward marginal regions of thezonenl relative to the longitudinal centerline l5 b=of the-covering l5 and av single layer or thickness oi such conductive composition at an intermediate region immediately at such center-line, whereby relatively higher temperaturesareprovidedatthe central zone I 9 along its intermediate regionas compared tothetemperatures atgitsmarginal regionsmoreremote from,

.i-such;centerline. Inthisxmanner, a heating action may: be such as to maintain said.intermediate region flthezone IS-free of ,'ic and `rloosen the "bundofii-e depnsnedi at: said. mafginai regions'V nin the spanwise direction, it is to be understood that such tubes may, if desired, extend wholly in the chordwise direction as shown especially inv Fig. 4, or may be disposed in part chordwise and in p art spanwise in any suitable arrangement thereof for obtaining the desired surface-configuration of the covering while maintaining the aerodynamic characteristics of the airfoil.

To the ends of obtaining the desired surfaceconguration at the distensible portions 22, 23 such that the desired stretching and stress for breaking the bond ofthe ice to the covering is provided; and also for distending the covering so as to loosen the ice and lift the latter sufficiently into the airstream for its removal by the scavenging action of such airstream while avoiding objectionable turbulent flow across the wing or airfoil, the tubes 28, 29 are desirably relatively small in diameter as compared to the inflatable tubes of prior constructions. The small tubes are effective to break the bond of the ice to the surface in cases where such prior constructions have lacked full effectiveness.

As to the size of the tubes effective to produce the improved ice-removing action, satisfactory results may be obtained where the diameter of thel tube passage is on the order of one-quarter (1/4) of an inch, and good results may also be obtained with tubes up to about one (l) inch in diameter. Tube sizes greater than about one inch may be less effective in removing strongly bonded ice for some icing conditions. i

Each of the spanwise tubes 28, 29 in the upper and lower rearward distensible portions 242,Y 23 is preferably less than about one (l) inch in diameter and each tube may be of uniform bore throughout its length. Inflatable tubes within the designated dimensional range make possible` of such ice to the covering and loosening andV breaking the ice-deposit free from the covering. The 4smallness of the tubes is further advantageous in that they may be arranged close together so that an appreciable number of tubesv are operative on a small zone of ice and diverse I v directions of the disrupting forces are obtained on a small area of ice spanning several adjacent tubes.

The improvement in the ice-removing action of the small tubes is noticeable especially where strongly adhered ice is deposited in a thin layer upon the surface of the covering; since with such small tubes, upon inflation and as soon as a crack' in the ice develops, the rubber material stretches in the crack and a high stress-concentration at the edge of the ice-piece results. The stress imposed by the inflation of such small tubes is greater than the strength of the adhesive bond and such loosening action combined with the relatively sharp curvature of each ridge causes the rubber to peel away from the ice deposit, which action continues unti1 the stress decreases to an extent such that the remaining stress in the rubber equals that of the vstrength of the adhesivez bond. s. Such .relatively high stressing action of the small tubes combined with the relatively sharp curvature of the surface deformations effectively loosensand breaks the ice deposited. Also, the tubes being relatively small project, upon ination, only a relatively short distance into the iioW of air and create little or no aerodynamic disturbance.

While the respective series of inflatable tubes 28, 29 may, if desired, be arranged' to have alternate tubes inflated simultaneously, all of theV at theirvinboard ends with an inflating manifold..

or conduit 30 of suitable reinforced rubber material extending in the chordwise direction across the tubes, and such manifold 30 is connected to a supply conduit 3l in communication with a source of air under pressure suitablyvlocatedwithin the aircraft structure. The other chordwise series of iniiatable tubes 29 beginning at the lower margin of the zone I9 are also desirably in communication at their inboard ends with an inating manifold 32 of suitable materialextending in thechordwise direction across such tubes, which manifold is connected to a supply conduit 33 in communication with the aforesaid source of air under pressure.

The fabric and rubber partsof the covering I5V are preferably united under vulcanization under heat and pressure., The respective spanwise margins 2 and 2| are preferably tapered in section for promoting smooth flow of air across the covering, as shown especially in Fig. l.

The covering I5, which may be marginally attached, is attached desirably to the leading edge of the airfoil by being adhered to such wing I6 continuously throughout the extent of the covering by a suitable adhesive 2l such, for example, as rubber cement. Such a mounting arrangement has the advantages of permitting only substantially outward expansion of the inflatable tubes facilitating distending and stretching the distensible portions at the outer surfaces thereof each into a plurality of closely-adjacent parallel ridges relatively sharply curved-in-section,Y and" of eliminating objectionable liftingy of the'cover ing from the airfoil at regions of low pressure rearwardly of the leading edge. The adhesive attachment also eliminates the necessity for additional marginal attaching structures such as metal reinforcing beads and fairing strips of prior constructions and the necessity for venting air from the space beneath the covering, thereby simplifying the construction of thev covering and facilitating providing a covering of light-weight and thinness. Such construction and mounting facilitates providing a relatively smooth outer surface of the covering whereby objectionable protuberances, which promote the local formation of ice, are avoided.

In the operation of the protective covering l5, the heating action at the central zone I9, which may be continuous or intermittent, makes possible Vtemperatures substantially uniform in the spanwise direction and varying chordwise in acfor effectively' preventing'the accumulation of tures by virtue of the insulating effect of ice relative to convection cooling of the covering by the airflow is effective for removing the various kinds of ice such as glaze ice, rime icev and rime frost,

especially at the stagnation zone or immediate leading edge region of the airfoil.

. Flow-back ice, which results from the melting of the ice at the central zone I9 and refreezing at the rearward distensible portions 22, 23, together with such ice-deposit as may be initially formed at such rearward portions, is removed upon ination of the respective series of inflatable tubes 28, 29, which inflation also dynamically unbalances any loosened ice remaining at the central zone I 9 facilitating the removal of the latter ice by the airflow. The simultaneous inflation of the tubes for each series thereof distends the surface of the covering into spanwise ridges of small radius of curvature at each rearward portion thereby imparting highly localized rupturing and stretching stresses at each of the tubes to the ice-deposit thereon effectively loosening such ice and lifting the same into the rapid laminar flow of air for removal by the scavenging action of such flow of air.

Insome cases, the rearward ice at zones 22, 23 by virtue of its thickness and total strength, may be broken loose in the form of relatively large chunks. Due to the localized and high stressing action of the inflated tubes, only a relatively narrow bonded zone as compared to the tube width may remain at each of the tubes, the intermediate regions of ice between such latter Zones being unadhered. The large chunks of ice, when lifted into the laminar flow of air, are blown away by the force of such flow of air. Such innation of the tubes also lifts and dynamically unbalances any remaining loosened ice-deposit spanning the heating Zone I9 for removal by the airflow. In this manner, the protective covering I effectively prevents the accumulation of ice upon the wing I6.

The modified construction 40 of the protective covering shown especially in Figs. 4 and 5 differs from the covering I5 in that inflatable tubes 4I, 42 and 43, 44 at rearward dstensible Zones or portions 45, 46 are arranged such that they extend substantially parallel with one another in the chordwise direction, and in that-a heating element 41 extending spanwise in a central heating zone 48 comprises two layers 49, 50 of suitable fabric reinforced conductive composition, each coextensve in length and width with one another and substantially coextensive with the heating zone 48, the heating element being disposed between the inner and outer faces of a suitable re silient rubber body 5I of the covering 4i).

The inflatable tubes 4I, -42 and 43, 44 are desirably each less than about one (1) inch in diameter and may be 1/2 inch in diameter; and extend chordwise in substantially adjoining relation to one another throughout their extent, the space between adjacent margins of adjacent tubes being less than the width of one of such adjacent tubes. The chordwise tubes are arranged in series spanwise and all of the tubes of each series at each portion 45, 46 may, if desired, be inflated l simultaneously; but preferably, alternate tubes are inflated in alternation in a cyclical manner with the other tubes of each aforesaid series and to this latter end, inilating manifolds 52, 53 and 54, are provided. Such manifolds are interconnected through conduits 56, 51 and 58, 59 with a suitable source of air under pressure for acl complishing such alternate inflation.

For-example, at the distensible portion A.45 the alternate inflatable tubes 4I are each in communication with the manifold 52 and the other tubes 42 are each in'communication with the manifold 53. Similarly, the alternate tubes 43 at the distensible portion 45 are each in communication with the manifold 55 and the other tubes 44 are each in communication with the manifold 54. In this manner, alternating inflation of alternate tubes in each series may be accomplished for distending the surface of the covering into chordwise-extending ridges in closely-adjacent parallel relation with one another throughout their extent, the ridges being relatively small and generally rounded-in-section whereby the desired relatively high and localized stresses are imparted to the ice deposited thereon to loosen the ice for removal by the airstrearn. Such alternate ination further provides a rocking action dynamically unbalancing the ice further facilitating its removal.

Since the stress created upon inflation of the tube increases in proportion to the rate of curvature of the tube Wall, better removal of ice at such rearward portions, as compared to that of relatively larger tubes, is obtained With the small vtubes having diameters within the designated range. Desirably, all of the tubes 4I to 44 are of uniform diameter relative to one anotherl and throughout their extent, thereby promoting uniformity of ice-removal action. Such tubes also provide the desired lifting action for placing the ice into the path of the rapid laminar flow. The

chordwise arrangement of the tubes is advantageous in minimizing turbulence of flow of air across the rearward portions 45, 45; sincesuch tubes extend generally parallel with the direction of the laminar flow of air. spanwise margins 60, 6I may be tapered in cross-section for facilitating smooth flow of air across the covering.

The heating element 41 at the central heating Zone 48 comprises a pair of sheets 49, 50 of suitable electrically-conductive resilient composition having a suitable fabric reinforcement therein, the sheets being positionedin superimposed relation to one another and substantially eoextensive with one another throughout the extent of such central zone 48. Suitable flexible braided conductor elements 52, B3 in substantially flat strip form are sandwiched between the sheets ofconductive material and extend spanwise along the heating zone adjacent the opposite spanwise mai'- gins of such zone. The conductor elements 62, 63 are desirably iixedly secured in place as by a suitable adhesive and by sewing engaging the reinforcing material of the conductive sheets 49 and 5i] and the material of the conductor elements 62, 63, such sewing preferably being along the inner margins of each conductor element 62, 63 with respect to the longitudinal center-line 40a of the covering, thereby effectively resisting lateral shifting and distortion of the conductor elements during the molding and curing operation. The heating element 41 is embedded in the resilient rubber body 5I between the inner and outer faces of the covering, as shown especially in Fig. 5. The respective fabric and rubber parts of the laction described hereinabove,

adjacent parallel relation to one another. covering alsoincludes heating elements 83 to 81 covering @are unitedpreferably by Vmolding and vulcani'zing under heat and pressure.

The covering 6s, which also may be mar- Vgiifiallyattached, is desirably adhesively'attached throughout .its entire extent to the airfoil or Vv virigl, which attachment eliminates the probv'lem of venting and facilitates outward bulging only of the inflatable tubes. Such bulging further promotes the desiredr sharpness of curvature Vfoftlie''ridges for effective removal of the. ice.

vInthe operation of the covering 4i), the heat- Ving actio'n at` va central zone may bev continuous (anti-'icingactiom or intermittent (de-icing action), the temperatures at such zone 43 being eective forv preventing the formation ofice and 'evaporating the water droplets, and/or'ior .iceremoval purposes. The heating at the central zone i8 may besuch that the temperatures may be'v'aried oruniform in the spanwise and/or the 'chordwise directions, and for the construction shown', the temperatures are desirably uniform both spanwise and chordwise substantially throughout the entire extent of the heating Zone 48. Floweback Water re-freezing at the distensible zones 45, 46 and any initial ice-deposit at such zones are removed by the cyclical ination of the inflatable tubes which,'by virtue of their eiectively lift, loosen 'and break the ice for removal by the rapid laminar-now of air. Such ination of the tubes :if

also lifts and dynamically unbalances any remaining `loosened ice-deposit spanning the heat- .ingzone 4B 'for removal by the airflow,

Another-modified .construction 65 of the protective covering, as shown especially in Fig. 6, L

has YaV plurality of alternately chordwise-arranged heating 'and 'distensible Zones 66 to 16, inclusive, extending spanwise .of the covering. Like the coverings l5 and 4Q, the'cove'ring 65 has a body' of suitable resilient rubber material and includes inflatable tubes 11 to 82, inclusive, extendingspanwise iny the respective distensible v.cones or portions 66, E8, 10, 12, 14, 16 in closely- The desirably of suitable resilient conductive composition having suitable fabric reinforcement therein extending spanvvise at the heating zones 'orportions 61, 69, 1l,'13-and 15, the respective heating elements each being desirably c'oexten- L.: -sive with the extent of each said heating portions. `The respective distensible and heating zones are relatively narrow in Width as compared to the distensible and heating zones of the coverings I5 and 40, thereby providing a plurality of nart 11, k82 of uniform diameter, Yarranged. in

chordwise series and having adjacent margins of adjacent tubes substantially adjoining one another.v The intermediate distensible portions 68, 10., 12, 14 each may have a pair of inflatable tubesH 1'8, 19, '80, 8l of uniform diameter, similarflyarranged, whereby all of 'the aforesaid tubes T11 to 82 inclusive 'make possible the desired surfacie 'cbnieur'aton 'Of 'ridges Vrelatively small 'in curvature, arranged 'in chordwise series 'at *spaced-apart positions across the covering.

'The tubes for all of the distensible `portions beV of uniformsize, Lor. thetubes, by v@ionesy maybe of graduated and decreasing size; inthe rearward .direction vwith respect Vto the longitudinal centerlme Gbav or the cover. Forexampla the adjacent innermost 'distensible portions "s, "l2 mayhavetubes about one (.1) inch in diameter, the other intermediate. distensible portions 58, 14 may have tubes :about threeyquarter (ai) inch in diameter, and the `outer rearward -distensiblei portions 66, i6 .may have tubes Vabout one-half (1/2). inchY in diameter. Such tube arrangement is advantageousin facilitating removal of relatively heavy iceroaps .at the immediate leading edgeregiono'f the wings together Witheectively removing sheet-like ice formations rearwardly ofthe immediate leading edge region of the Wings, while vavoiding objectionable disturbance of the smooth flow ofi-air across the cover-ing, when such tubes are inated. It will be appreciated that this arrangement using relatively small tubes is Yalsoeffective in its ice-removal action; since-the stress imparted to the ice is in proportion to the rate of curvature of the tube, under-inflation, and such relatively high localized stretching and stresses at the respective spaced-apart distensible zones not only break the bond of theV ice but also loosen the'ice iorV removal by the airflow.

For inl-rating purposes, each group of tubes in the respective distensible portions is provided with an infiating manifold 88 to 93, inclusive, lwhich manifolds are connected by suitable conduits 94 to S9, inclusive, te a suitable source of air under pressure. The arrangement is such that all of the tubes in each of the distensible portionsare inflated simultaneously, and the respective groups of 'tubes insuch distensiblepertions may beinfiated simultaneously, or in al ternation to one another with respect to the longitudinal center 65a of the covering, lcrV in alternate sequenceacross the covering, or in any other desired manner- The heating .elements '83 to I inclusive, are imbedded inthe rubber .body of 'the covering e5 at the respective Aheating zones or portions 61, 69, "1l, 13 and 15, each heating element being substantially :coextensive in length and. width with the extent of such heating portions for providing temperatures efieetive'for ice-removal and/or icefprevention purposes. Each heating element desirably includes a pair of superimposed layers of suitable electrically-conductive composition having a suitable fabric reinforcernent'therein, and each includes a pair vof suitable ilexible braided conductor 'elements {65 to H4, inclusive, extending spanwise adjacent the opposite margins of the distensible portions and sandwiched lbetween the aforesaid layers. Each of the conductor elements |95 to llt are lixedly secured'as by'a suitable adhesive and `by sewing extending through the material of the fabric reinforcement and the material of the conductors per se'. Such sewing beine disposed adjacent the inner margin of each conductor element with respect to the longitudinal center-line `65a, of the covering for resisting lateral distortion Aand 'shifting of 'the conductor elements during the molding operation,

The Opposite spanwise `margins o f'the covering are desirably tapered in section `to facilita-,te smooth 119W '0i 'air 'across the covering The rubber and fabricparts of the 'cover 65 are desirably united by molding and vulcanizing under 'heat and pressure. The covering 65 is also desirably 75 adhesively vattached to the Wing substantially fascetta "continuously throughout the entire extent ci the yleading edge, and/or loosen the ice-deposits adhering to the covering at such heating zones.'

Theiniiation of the inatable tubes loosens and breaks the ice at the respective'distensible portions and also lifts loosened ice-formations spanning the respective heating zones into the path oi the flow of air dynamically unbalancing the f same for removal by such air. Y In this manner, the respective distensible and heating actions cooperate in effectively preventing thel accumulation of ice on the covering 65.

A still further modified construction |40 of the resilient rubber protective covering, as shown especially in Fig. '1, includes a plurality of alternate heating and distensible zones |4| to |45 extending spanwise substantially throughout the entire extent of the covering, which zones or por- 1 tions |4| to |45 may be relatively wide as compared to the zones of the construction 65 shown especially in Fig. 6. Each heating zone or portion 4|, |43, |45 has a suitable heating element |46, |41,'|48 of reinforced conductive composii tion desirably embedded in the rubber material of the covering for providing substantially uniform temperatures spanwise and chordwise throughout the entire extent of such heating portions, but thev temperatures at the center element |41 may be higher than those at the rearward elements |46, |48. Also, each heating element is provided with a pair of spaced-apart flexible braided contacter elements |49-|50, |5|-|52,

|53-I54, suitably fixedly secured as by sewing f to such heating element, which sewing extends continuously along the inner margins of the conductor elements with respect to the longitudinal centerline |40a of the covering for preventing lateral shifting and distortion of such conductor elements.

Each distensible portion |42, |44 has a plurality of relatively small inflatable tubes |55, |5t,

each less than about one (l) inch in diameter, for providing the desired surface-configuration oi ridges, upon inflation thereof. The inflatable tubes |55', |56 extend Y spanwise substantially throughout the entire extent of the distensible portions |42, 44 and are positioned such that adjacent margins of adjacent tubes are substantially contiguous with one another throughout their entire extent. For simultaneous inflating purposes, a suitable manifold |51, |58 is in communication with each chordwise series of inilatable tubes. The manifolds |51, 58 are connected to a source of air under pressure by suitable conduits |59, |50 in communication with such manifolds.

The covering |40 may have spanwise margins 6| |B2 tapered in section and may be adhesively attached throughout its entire extent to the airfoil. When so mounted on the airfoil, the covering |40 is arranged such that the central heating zone |43 is at the stagnation zone or immediate leading edge region of such airfoil.

' nel'.

l In the operation of the covering |40, the heating zones may be heated continuously or intermittently as described hereinabove, and have desirably substantially uniform temperatures throughout the heating zones for effective iceremoval purposes. Intermittent operation of the heating zones at relatively low temperatures eliminates the problem of now-back. series'of tubes |45, |46 may be inflated intermittently or coincidentally and in a cyclical man- Such inflation of the tubes provides the desired surface-configuration having a plurality of relatively small sharply-curved-in-section 'ridges in closely-adjacent parallel relation to one another throughout their extent. 'I'he iceremoving action of the tubes is substantially like that described for the inflatable tubes of the protective covering 20.

The invention thus makes possible new and useful protectiveV coverings of elastic material having various arrangements of heating and distensible zones, which coverings are effective in preventing the accumulation of ice on the leading edges of airfoils by virtue of the cooperative action of their elements in a new relationship. The invention also makes possible the selection of a particular covering arrangement best fitted to cope with one or more kinds of icing conditions, which may be encountered in the operation of aircraft; and the selection of a particular covering arrangement best ntted to cope with the iceforxnations which occur on streamline bodies or airfoils of diiierent profiles and thicknesses. Such coverings also have further advantages in that they facilitate the provision of smooth surfaces abcut the leading edge, eliminate the diiicult problem of venting, facilitate the attachment to the airfoil, and which are characterized by their thinness and light-weight construction and convenience of manufacture.

Variations may be made without departing from the scope of the invention as it is defined in the following claims.

I claim:

1. Apparatus for preventing the accumulation of ice on the leading edge of an airfoil, said apparatus comprising a unitary covering member having at least one spanwise-extending distensible surface portion for disposition at a rearward area of said leading edge and one spanwiseextending non-distensible portion adjacent the vfirst said portion for disposition at the frontal area of said leading edge, the distensible portion comprising a plurality of spanwise-extending iniiatable tubular passages each less than about one inch in diameter disposed in said member in closely adjacent parallel relation one to another iniiatable to provide under iniiation a plurality of sharply curved spanwise-extending ridges at the surface of said distensible portion for breaking the adhesive bond of overlying ice at said rearward area of the leading edge, means for inating said tubular passages to distend said surface of the distensible portion into said spanwise-extending ridges without distending the adjacent non-distensible portion, and means in and constituting a part of said non-distensible portion of said member for heating the surface thereof at said frontal area to interrupt the continuity of ice deposited on said member.

2. Apparatus for preventing the accumulation of ice on the leading edge of an airfoil, said apparatus comprising a unitary covering member having at least one spanwise-extending distensible Asurface portion for disposition at a rear- Each ber having distensible surface portions spacedapart for disposition at the rearward areas of said leading edge and a non-distensible surface portion intermediate said portions for disposition at the frontal area of said leading edge, means imbedded in the intermediate non-distensible portion of said member for heating the surface at said frontal area to interrupt the continuity of ice deposited about the leading edge, and a plurality of inflatable tubular passages in said member at each of said distensible portions for distending the surface in said rearward areas to loosen ice rearwardly of the interruption in the ice at said frontal area.

9. Apparatus for preventing the accumulation of ice upon the leading edge of an airfoil, said apparatus comprising a unitary covering member of elastic material having distensible surface portions spaced-apart for disposition at the rearward areas of said leading edge and a nondistensible surface portion intermediate said portions for disposition at the frontal area of said leading edge, electrical heating means im- 18 bedded in the elastic material of the intermediate non-distensible portion of said member for heating the surface at said frontal area to interrupt the continuity of ice deposited about the leading edge, and a plurality of spanwiseextending inflatable tubular passages in said member at each of said distensible portions for distending the surface in said rearward areas to loosen ice rearwardly of the interruption in the ice at said 'frontal area.

BENJAMIN F. JONES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,168,012 Waner Aug. 1, 1939 2,393,635 y Hubbard Jan. 29, 1946 2,401,247 Hunter May 28, 1946 2,418,205 Taylor Apr. 1, 1947 2,436,889 Heston Mar. 2, 1948 

